In a Saturday night tweet, Musk said an upgraded SpaceX/Tesla pod would be sped up to half of Mach 1, which is the speed of sound or about 767 mph (1,235 km/h), and then stopped, all within about three quarters of a mile (1.2 kilometers).

That's like laying down a track that's about as long as four or five Manhattan city blocks and accelerating a vehicle down it until it reaches about 380 mph (612 km/h), then hoping you can slow it back down to a complete stop before it hits the end of the track.

Tesla and SpaceX, along with another Musk venture, The Boring Company, all seem to be contributing some resources to the Hyperloop side project. A pair of startups, the Richard Branson-led Virgin Hyperloop One and Hyperloop Transportation Technologies, have been leading the charge in getting the technology off the ground, but Musk has also been developing it himself.